Monodispersed photographic reversal emulsions



United States Patent 3,501,305 MONODISPERSED PHOTOGRAPHIC REVERSAL EMULSIONS Bernard D. Illingsworth, Rochester, N.Y., assignor t0 Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 533,440, Mar. 11, 1966. This application Mar. 2, 1967, Ser. No. 619,948

Int. Cl. G03c 1/28 US. Cl. 96108 25 Claims ABSTRACT OF THE DISCLOSURE Direct-positive photographic emulsions comprising silver halide grains which are monodispersed. Grains of this type which generally exhibit a substantially uniform diameter, are disclosed. Such emulsions can contain electron acceptors and can be fogged with both reduction and gold fogging agents. Photographic elements employing such emulsions and processes for preparing them are also disclosed.

This application is a contiuuation-in-part of Illingsworth, U.S. application Ser. No. 533,440, filed Mar. 11, 1966, and entitled Photographic Reversal Emulsions.

This invention relates to photographic materials, their preparation and use. In one of its aspects, this invention relates to direct-positive photographic emulsions and elements comprising fogged silver halide grains and a compound which accepts electrons. In another of its aspects, this invention relates to direct-positive photographic silver halide emulsions and elements comprising reduction and gold fogged silver halide grains of substantially uniform diameter.

It is known that direct-positive images can be obtained with certain types of photographic silver halide reversal emulsions. As shown in British Patent 723,019, published Feb. 2, 1955, one photographic emulsion of this type is a photographic emulsion comprising an electron trapping compound and silver halide grains which are fogged with a combination of a reducing agent and a gold compound or a compound of a metal more electropositive than silver, such as, for example, palladium or platinum. However, in the past, direct-positive photographic silver halide emulsions comprising fogged silver halide grains, particularly those silver halide grains fogged using a combination of fogging agents as disclosed in British Patent 723,019, have not exhibited the high speed required for many applications in photography. It is evident, therefore, that a means for increasing the photographic speed of direct-positive photographic emulsions comprising fogged silver halide grains would substantially enhance the art.

Accordingly, it is an object of this invention to provide direct-positive photographic emulsions exhibiting increased photographic speed.

Another object of this invention is to provide a means for obtaining fogged direct-positive photographic silver halide emulsions and elements which comprise silver halide grains having a substantially uniform diameter frequency distribution.

Still another object of this invention is to provide a means for obtaining fogged direct-positive photographic silver halide emulsions and elements comprising electron trapping compounds such as cyanine dyes.

Still another object of this invention is to provide improved photographic reversal emulsions obtained by combining a low level of reduction fogging with a low level of gold fogging of photographic silver halide grains having a substantially uniform grain size.

Other objects and advantages of the invention will become apparent from an examination of the specification and claims which follow.

The above and other objects of this invention are obtained with direct-positive photographic silver halide emulsions comprising fogged silver halide grains which have a uniform diameter frequency distribution, i.e., silver halide grains which have substantially the same diameter. Such direct-positive photographic silver halide emulsions can be termed monodispersed direct-positive photographic silver halide emulsions. These photographic emulsions exhibit a significant increase in speed in comparison to direct-positive photographic silver halide emulsions which are not monodispersed.

One embodiment of this invention relates to a directpositive photographic emulsion comprising fogged silver halide grains, at least by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

Another embodiment of this invention relates to a direct-positive photographic emulsion comprising reduction and gold fogged silver halide grains and a compound which accepts electrons, at least 95 by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

Another embodiment of this invention relates to a photographic element comprising a support and at least one photographic silver halide layer which comprises fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter.

Another embodiment of this invention relates to a photographic element comprising a support and at least one photographic silver halide layer which comprises reduction and gold fogged silver halide grains and a compound which accepts electrons, at least 95%, by weight, of said grains having a diameter which is within about 40% of the mean grain diameter, the concentration of reduction fogging agent employed to fog said grains being in the range of about 0.0005 to about 0.06 milliequivalent per mole of silver halide.

Still another embodiment of this invention relates to the process which comprises contacting (1) silver halide grains, at least 95 by weight, of which have a diameter which is within about 40% of the mean grain diame ter, with (2) about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent (3) at a temperature in the range of about 40 to about degrees C., the ratio of gold fogging abent to reduction fogging agent being in the range of about 1:3 to about 20:1.

The direct-positive photographic emulsions of this invention comprise fogged silver halide grains having a substantially uniform diameter. Generally, in such emulsions, no more than about 5%, by weight, of the silver halide grains smaller than the mean grain size and/ or no more than about 5%, by number, of the silver halide grains larger than the mean grain size, vary in diameter from the mean grain diameter by more than about 40%. Preferred direct-positive photographic emulsions of this in- Patented Mar. 17, 1970 vention comprise fogged silver halide grains, at least 95%, by weight, of said grains having a diameter which is within 40%, preferably within about 30%, of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., such as projective area as shown in an article by Trivelli and Smith entitled Empirical Relations Between Sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, vol. LXXIX, 1939, pp. 330-338. The aforementioned uniform size distribution of silver halide grains is a characteristic of the grains in monodispersed photographic silver halide emulsions. Silver halide grains having a narrow size distribution can be obtained by controlling the conditions at which the silver halide grains are prepared using a double run procedure. In such a procedure, the silver halide grains are prepared by simultaneously running an aqueous solution of a water soluble silver salt, for example, silver nitrate, and a water soluble halide, for example, an alkali metal halide such as potassium bromide, into a rapidly agitated aqueous solution of a silver halide peptizer, preferably gelatin, a gelatin derivative or some other protein peptizer. The pH and the pAg employed in this type of procedure are inter-related. For example, changing one while maintaining the other constant at a given temperature can change the size frequency distribution of the silver halide grains which are formed, as shown in Example 1. However, generally the temperature is about 30 to about 90 degrees C., the pH is up to about 9, preferably 4 or less and the pAg is up to about 9.8. Suitable methods for preparing photographic silver halide emulsions having the required uniform particle size are disclosed in an article entitled Ia: Properties of Photographic Emulsion Grains, by Klein and Moisar, The Journal of Photographic Science, vol. 12, 1964, pp. 242-251; an article entitled The Spectral Sensitization of Silver Bromide Emulsions on Different Crystallographic Faces by Markocki, The Journal of Photographic Science, vol. 13, 1965, pp. 85-89; an article entitled Studies on Silver Bromide Sols, Part I. The formation and Ageing of Monodisperse Silver Bromide Sols by Ottewill and Woodbridge, The Journal of Photographic Science, vol. 13, 1965, pp. 98-103 and an article entitled Studies on Silver Bromide Sols, Part II. The Effect of Additives on the S01 Particles by Ottewill and Woodbridge, The Journal of Photographic Science, vol. 13, 1965, pp. 104-107. A preferred class of photographic silver halide emulsions employed in the practice of this invention contains silver halide grains in which (1,0,0) faces predominate. Such silver halide grains are referred to herein as cubic regular grains. These cubic regular grains can be prepared by carrying out the aforementioned double run procedure so that the pAg is maintained in the range of about 7.1 to about 9.2. The pAg employed can change with the particular silver halide prepared. For example, the silver bromoiodides are generally prepared at a pAg in the range of about 8.6 to about 9.2, the silver chlorobromides at about 7.9 and the silver chlorides at about 7.1. The pH is maintained at about 4 or less during the preparation with sulfuric or an equivalent acid. Quantities of halide ion greatly in excess of silver ion in the mass are also avoided.

The direct-positive photographic silver halide emulsions of this invention contain silver halide grains which are fogged. Fogging can be effected by chemically or physically treating the photographic silver halides by methods previously described in the prior art. Such fogging can be accomplished by various techniques such as chemical sensitization to fog, particularly good results being obtained with techniques of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, vol. XXVIII, January 1957, pp. 57 to 65. The silver halide grains can be fogged with the high intensity light, reduction fogged with a reducing agent such as thiourea dioxide or stannous chloride or fogged with gold or noble metal compounds. Combinations of reduction fogging agents with gold compounds or compounds of another metal more electropositive than silver, e.g., rhodium, platinum, or iridium, can be used in fog ging the silver halide grains. The fogged silver halide grains in the direct-positive photographic emulsions of this invention give a density of at least 0.5, when developed without exposure for five minutes at 68 degrees F. in Kodak DK-SO developer when a direct-positive emulsion containing such grains is coated at a coverage of 50 to about 500 mg. of silver per square foot of support.

The direct-positive photographic emulsions of this invention can comprise reduction and gold fogged silver halide grains, i.e., silver halide grains which are fogged with a combination of a reduction fogging agent and a gold fogging agent. The use of low concentrations of reduction and gold fogging agents in such a combination give unique fogged silver halide grains which are characterized by a rapid loss of fog upon chemical bleaching, as described hereinafter. It is known that one equivalent weight of a reducing agent will reduce one equivalent weight of silver halide to silver. To obtain the fogged silver halide grains which are characterized by a rapid loss of fog upon bleaching, much less than one equivalent weight of reduction fogging agent is employed. Thus, less than about 0.06 -milliequivalent of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains. Generally, about 0.0005 to about 0.06, preferably about 0.001 to about 0.03 milliequivalent of reduction fogging agent per mole of silver halide is employed in fogging the silver halide grains in the practice of this invention. Higher concentrations of reduction fogging agent can result in a substantial loss in photographic speed. A preferred reduction fogging agent employed in combination with the gold fogging agent, or a compound of another metal more electropositive than silver, is thiourea dioxide which is preferably employed in a concentration in the range of about 0.05 to about 3, most preferably about 0.1 to about 2 milligrams per mole of silver halide or about 0.005 to about 0.03 millimole per mole of silver halide. Stannous chloride is another suitable reduction fogging agent which is used in practicing this invention and is preferably used in concentrations in the range of about 0.05 to about 3 milligrams of stannous chloride per mole of silver halide. The use of the reduction and gold fogging agents in low concentration gives direct-positive photographic silver halide emulsions exhibiting outstanding photographic speed. Examples of suitable reduction fogging agents which can be employed in the practice of this invention include hydrazine, phosphonium salts such as tetra(hydroxy methyl) phosphonium chloride, thiourea dioxide, as disclosed in Hillson U.S. Patent 3,062,651, issued Nov. 6, 1962, and Allen et al. U.S. Patent 2,983,609, issued May 9, 1961, reducing agents such as the stannous salts, e.g., stannous chloride, as disclosed in Carroll U.S. Patent 2,487,850, issued Nov. 15, 1939, polyamines suchas diethylene triamine, as disclosed in Lowe et al. U.S. Patent 2,519,698, issued Aug. 15, 1950, polyamines such as spermine as disclosed in Lowe et al. U.S. Patent 2,521,925, issued Sept. 12, 1950, bis(B-aminoethyl) sulfide and its water soluble salts as disclosed in Lowe et al. U.S. Patent 2,521,926, issued Sept. 12, 1950, and the like.

The gold fogging agents employed in practicing this invention can be any gold salt suitable for use in fogging photographic silver halide grains and includes the gold salts disclosed in Waller et al. U.S. Patent 2,399,083, issued Apr. 23, 1946, and Damschroder et al. U.S. Patent 2,642,361, issued June 16, 1953. Specific examples of gold fogging agents are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride, 2-aurosulfobenzothiazole metho chloride, and the like. The concentration of gold fogging agent employed in the practice of this invention is subject to variation, but is generally in the range of about 0.001 to about 0.01

millimole per mole of silver halide. Potassium chloroaurate is a preferred gold fogging agent and is often used at concentrations of less than about mg. per mole of silver halide and preferably at concentrations in the range of about 0.5 to about 4 milligrams per mole of silver halide. When a gold fogging agent is used in combination with a reduction fogging agent, the gold fogging agent preferably comprises a major portion of the fogging combination with the ratio of gold fogging agent to reduction fogging agent generally being in the range of about 1:3 to about 20:1, often about 2:1 to about 20:1. The silver halide grains are preferably fogged using the reduction fogging agent initially and subsequently using the gold fogging agent. However, the reverse order of agents can be used or the reduction and gold fogging agents can be used simultaneously.

In practicing this invention, the silver halide grains can be fogged prior to coating or they can be coated prior to fogging. The reaction conditions during fogging of the silver halide grains are subject to wide variation although the pH is generally in the range of about 5 to about 7, the pAg is generally in the range of about 7 to about 9 and the temperature is generally in the range of about 40 to about 100 degrees C., most often about 50 to about 70 degrees C. During fogging the silver halide grains can be suspended in a suitable vehicle such as gelatin which is generally employed at a concentration in the range of about 50 to about 200 grams per mole of silver halide.

As previously indicated, the most desirable photographic speed is exhibited by direct-positive photographic emulsions comprising silver halide grains which have a substantially uniform diameter frequency distribution and which are fogged using low concentrations of reduction fogging agents and gold fogging agents in combination. Such silver halide grains are characterized by a rapid loss of fog upon chemical bleaching. These grains will lose at least about 25% and generally at least about 40% of their fog when bleached for ten minutes at 68 degrees F. in a potassium cyanide bleach composition as described hereinafter. This fog loss can be illustrated by coating the silver halide grains as a photographic silver halide emulsion on a support to give a maximum density of at least 1.0 when processed for 6 minutes at about 68 degrees F. in Kodak DK50 developer and comparing the density of such a coating with an identical coating which is processed for 6 minutes at 68 degrees F. in Kodak DK-SO developed after being bleached for about 10 minutes at 68 degrees F. in the potassium cyanide bleach composition. The maximum density of the unbleached coating will be at least 30% greater, generally at least 60% greater than the maximum density of the bleached coating. Kodak DK-50 developer is described in the Handbook of Chemistry and Physics, 30th edition, 1947, Chemical Rubber Publishing 00., Cleveland, Ohio, p. 2558, and has the following composition:

Water, about 125 degrees F. (52 degrees C.)-500 cc. N-methyl-p-aminophenol sulfate2.5 grams Sodium sulfite, desiccated30.0 grams Hydroquinone2.5 grams Sodium metaborate10.0 grams Potassium bromide0.5 gram Water to make 1.0 liter.

One embodiment of this invention relates to directpositive photographic emulsions which comprise not only silver halide grains having a substantially uniform size frequency distribution, 'but also a compound which accepts electrons. Suitable electron accepting compounds include the photoelectron accepting compounds or desensitizing dyes often used in photographic reversal systems. Compounds of this type include the known desensitizers which trap electrons, as disclosed in British Patent 723,019, published Feb. 2, 1955. The electron acceptors which give particularly good results in the practice of this invention can be characterized in terms of their polarographic halfwave potentials, i.e., their oxidation reduction potentials determined by polarography. Cathodic measurements can be made with a 1 10 molar solution of the electron acceptor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mecury electrode with the polarographic halfwave potential for the most positive cathodic wave being designated E Anodic measurements can be made with 1 10 molar aqueous solvent solution, for example methanolic solutions of the electron acceptor which are 0.05 molar in sodium acetate and 0.005 molar in acetic acid using a carbon paste of pyrolytic graphite electrode, with the voltametric half peak potential for the most negative anodic response being designated E,,. In each measurement, the reference electrode can .be an aqueous silversilver chloride (saturated potassium chloride) electrode at 20 degrees C. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; Polarography, by Koltholf and Lingane, 2nd ed., Interscience Publishers, New York, N.Y., 1952; Analytical Chemistry, 36, 2426 (1964) by Elving; and Analytical Chemistry, 30, 1576 (1958) by Adams. Plus and minus signs are according to IUPAC (International Union of Pure and Applied Chemistry) Stockholm Convention 1953. Compounds which can be employed as electron acceptors in the practice of this invention include organic compounds having an anodic polarographic halfwave potential (E,,) and a cathodic polarographic potential (E which when added together give a positive sum. Preferably, such compounds also spectrally sensitize photographic silver halide emulsions to radiation having a wavelength of at least about 480 m and generally spectrally sensitize such emulsions in the range of about 480 to about 800 mu. Advantageously, these compounds provide spectral sensitization such that the ratio of minus blue relative speed to blue relative speed is greater than 7 and preferably greater than 10 when exposed to a tungsten source through Wratten No. 16 and No. 35 plus 38A filters respectively and can be termed specral sensitizing electron acceptors.

An especially useful class of electron accepting compounds which can be used in the direct-positive photographic silver halide emulsions of this invention are cyanine dyes; particularly imidazoquinoxaline dyes, such as those described in Brooker et al., Belgian Patent 660,253, published Mar. 15, 1965. Very good results are obtained with cyanine dyes containing an indole nucleus aromatically substituted in the 2 position, i.e., a cyanine dye containing a 2-aromatically substituted in dole nucleus. One useful class of spectral sensitizing electron acceptors are the bis-(l-alkyl-2-phenyl-indole-3) trimethine cyanines described by Coenen et al., US. Patent 2,930,694, isued Mar. 29, 1960. Another useful class of dimethine cyanine dyes of this type is disclosed in British Patent 970,601.

The compounds which accept electrons in the directpositive photographic silver halide emulsions of this invention can be employed in widely varying concentrations. However, such compounds are preferably employed at concentrations in the range of about milligrams to about 2 grams of electron acceptor per mole of silver halide. Specific examples of suitable electron acceptors include:

I 1 Me Me B re (2) 2,2-Di-p-methxypl1eny1-1,1-dimethyl-3,3'-indolocarbocyanine bromide 0 Me M60 (3) 1,1-Dimctl1yl-2,2,8-tripl1enyl-3,3-intlolocarbocyani11c perchlorate (4) 1,1-3,3'-Tetraethylimidazo [4 b] quinoxalinocarbocyanine chloride Additional examples include phenosafranine, pinacryptol yellow, 5-m-nitrobenzylidenerhodanine, S-m-nitrobenzylidene-3-phenylrhodanine, 3-ethyl-S-m-nitrobenzylidenerhodanine, 3-ethyl-5'-(2,4-dinitrobenzylidene)rhodanine, 5-0- nitrobenzylidene-3-phenylrhodanine, 1,3-diethyl-6-nitrothia-2'-cyanine iodide, 4-nitro-6-chlorobenzotriazle, 3,3- diethyl-6,6-dinitro-9-phenylthiacarbocyanine iodide, 2- (p-dimethylaminophenyliminomethyl)benzothiazole ethoethyl sulfate, crystal violet, 3,3-diethyl-6,6'-dinitrothiacarbocyanine ethyl sulfate, 1,3-di-ethyl-6-nitrothia-2'-cyanine iodide, 1,3-diamino-5-methyl-phenazinium chloride, 4-nitro-6-chlorobenzotriazole, 3,3-di-p-nitrobenzylthiacarbocyanine bromide, 3,3-di-p-nitrophenylthiacarbocyanine iodide, 3,3-di-o-nitrophenylthiacarbocyanine perchlorate, 3,3'-dimethyl-9-trifiuoromethylthiacarbocyanine iodide, 9- (2,4-dinitrophenylmercapto 3 ,3 '-diethylthiacarbocyanine iodide, bis(4,6 diphenylpyryl 2)trimethinecyanine perchlorate, anhydro-2-p-dimethylaminophenyliminoethyl-6- nitro-3-(4-sulfobutyl)benzothiazolium hydroxide, 1-(2- benzothiazolyl) -2- (p-dimethylaminostyryl 4,6-diphenylpyridinium iodide, 1,3-diethyl-5-[1,3-neopentylene-6-(1,3, 3-trimethyI-Z-indolinylidene)-2,4-hexadienylidene] 2-thiobarbituric acid, 2,3,5-triphenyl-2H-tetrazolium chloride, 2- (4-iodophenyl)-3-(4-nitrophenyl) 5 phenyl tetrazolium chloride, l-methyl-8-nitroquinolinium methyl sulfate, 3,6- bis[4-(3-ethyl-2-benzothiazolinylidene)- 2- butenylidene]- 1,2,4,5-cyclohexanetetrone and the like.

The silver halides employed in the preparation of the photographic compositions described herein include any of the photographic silver halides as exemplified by silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide, silver chlorobromide, and the like. Silver halide grains having a mean grain diameter, i.e., an average grain size in the range of about .01 to about 2 microns, preferably about .02 to about 1 micron, give particularly good results. The silver halide grains can be any suitable shape such as cubic or octahedral, but they are preferably cubic, and more preferably cubic-regular. The preferred photographic silver halide emulsions comprise at least 50 mole percent bromide, the most preferred emulsions being silver bromoiodide emulsions, particularly those containing less than about ten mole percent iodide. The photographic silver halides can be coated at silver coverages in the range of about 50 to about 500 milligrams of silver per square foot of support.

Various colloids can be used as vehicles or binding agents in the direct-positive photographic materials of this invention. Satisfactory colloids which can be used for this purpose include any of the hydrophilic colloids generally employed in the photographic field, including, for example, gelatin, colloidal albumin, polysaccharides, cellulose derivatives, synthetic resins such as polyvinyl compounds, including polyvinyl alcohol derivatives, acrylamide polymers and the like. In addition to the hydrophilic colloids, the vehicle or binding agent can contain dispersed polymerized vinyl compounds, particularly those which increase the dimensional stability of photographic materials. Suitable compounds of this type include water-insoluble polymers of alkyl acrylates or methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates and the like.

The photographic compositions described herein can be coated on a wide variety of supports in preparing photographic elements. The photographic silver halide emulsions can be coated on one or both sides of the support which is preferably transparent and/or flexible. Typical supports are cellulose nitrate film, cellulose ester film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and other polyester film as well as glass, paper, metal, Wood and the like. Supports such as paper which are coated with a-olefin polymers, particularly polymers of u-olefins containing two or more carbon atoms, as exemplified by polyethylene, polypropylene, ethylene-butene copolymers, and the like, give good results.

The photographic silver halide emulsion and other layers present in the photographic elements made according to the invention can be hardened with any suitable hardener, including aldehyde hardeners such as formaldehyde, and mucochloric acid, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oXy starch or oxy plant gums, and the like.

The photographic silver halide emulsion layers can contain additional additives, particularly those known to be beneficial in photographic emulsions, including, for example, lubricating materials, stabilizers, speed increasing materials, absorbing dyes, plasticizers, and the like. These photographic emulsions can also contain spectral sensitizing dyes in addition to the electron accepting compounds which can spectrally sensitize in some cases. Suitable spectral sensitizers include the cyanines, merocyanines, complex(trinuclear)cyanines, complex(trinuclear) merocyanines, styryls and hemicyanines. Furthermore, these emulsions can contain color forming couplers or can be developed in solutions containing couplers or other color generating materials. The color forming couplers can be incorporated into the direct positive photographic silver halide emulsion using any suitable technique, e.g., techniques of the type shown in Ielley et al., U. S. Patent 2,322,027, issued June 15, 1943; Fierke et al., US. Patent 2,801,171, issued July 30, 1957; Fisher, US. Patents 1,055,155 and 1,102,028, issued Mar. 4, 1913 and June 30, 1914, respectively, and Wilmanns, US. Patent 2,186,849, issued Jan. 9, 1940. They can also be developed using incorporated developers such as polyhydroxy 'benzenes, aminophenols, 3-pyrazolidones, and the like.

It is sometimes advantageous to employ surface active agents or compatible mixtures of such agents in the preparation of the photographic materials described herein. Suitable agents of this type include non-ionic, ionic and amphoteric types, as exemplified by polyoxyalkylene derivatives, amphoteric amino acid dispersing agents, including sulfobetaines, and the like. Such surface active agents are described in US. Patent 2,600,831, issued June 17, 1952; US. Patent 2,271,622, issued Feb. 3, 1942; US. Patent 2,271,623, issued Feb. 3, 1942; US. Patent 2,275,727, issued Mar. 10, 1942; US. Patent 2,787,604, issued Apr. 2, 1957; US. Patent 2,816,920, issued Dec. 17, 1957; US. Patent 2,739,891, issued Mar. 27, 1956 and Belgian Patent 652,862.

This invention can be further illustrated by the following examples of preferred embodiments thereof although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

EXAMPLE I Monodispersed fogged direct-positive photographic silver halide emulsions exhibit substantial increases in photographic speed in comparison to non-monodispersed fogged direct-positive photographic silver halide emulsions. Furthermore, the silver halide grains in the monodispersed fogged direct-positive photographic emulsions can be cubic regular. To illustrate each of these features, the following photographic silver halide emulsions are prepared:

Emulsion A A cubic regular monodispersed silver bromoiodide photographic emulsion containing approximately 2.5% iodide and having an average grain size of about 0.2 micron is prepared by adding (1) an aqueous solution of potassium bromide and potassium iodide and (2) an aqueous solution of silver nitrate, simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 degrees C. over a period of about 35 minutes. The pH is maintained at about 2 during precipitation and the pAg is about 9. The emulsion is chillset, shredded and washed by leaching with cold water in the conventional manner.

Emulsion B A cube-octahedral monodispersed silver bromoiodide photographic emulsion is prepared using the procedure employed for Emulsion A except that the pAg is maintained at about 9.4 during the formation of the silver halide grains. In each of Emulsions A and B at least 95%, by weight, of the silver halide grains have a diameter which is within about 40% of the mean grain diameter, i.e., the average grain size of 0.2 micron.

Emulsion C A non-monodispersed silver halide photographic emulsion is prepared using the procedure employed for Emulsion A except that the pH is maintained at 8 during the silver halide grain formation. The resulting emulsion has an average grain size similar to that of Emulsions A and B. However, the size frequency distribution is considerably broader; i.e., only 70%, by weight, of the grains, have a diameter which is within 40% of the mean grain diameter.

Each of the photographic Emulsions A, B and C is reduction and gold fogged by first adding 0.2 mg. of thiourea dioxide and heating for 60 minutes at 65 degrees C. and then adding 4.0 mg. of potassium chloroaurate and heating for 60 minutes at 65 degrees C. One-hundred mg. of an electron accepting compound (-m-nitrobenzylidenerhodanine) per mole of silver halide is added to each emulsion. Samples of each of the Emulsions A, B, and C are coated on cellulose acetate film support at coverages of 100 mg. of silver and 250 mg. of gelatin per square foot of support. A sample of each coating is exposed on an Eastman Ib sensitometer, developed for 6 minutes in Kodak DK-50 developer, fixed, washed and dried. The maximum density, photographic speed at a given density below maximum density and gamma are determined using the same procedure for each coating. The results are as follows:

TABLE 1 Emulsion coating Dm, Relative speed Gamma It can be seen from the above results that the use of silver halide grains of substantially uniform diameter frequency in fogged direct-positive photographic silver halide emulsions (Emulsion Coatings A and B) gives a substantial increase in photographic speed. Furthermore, it can be seen from the above table that the use of cubic regular silver halide grains in such emulsions (Emulsion Coating A) significantly increases contrast.

Similar results are obtained when the above procedure is repeated with fogging agents such as hydrazine, tetra- (hydroxymethyl)phosphonium chloride, triethylenetetramine and gold or noble metal fogging agents such as potassium aurithocyanate, 2-aurosulfobenzothiazole metho chloride, ammonium hexachloro palladate and the like.

EXAMPLE II As previously indicated, the silver halide grains which are fogged with a combination of a low concentration of reduction fogging agent and noble metal fogging agent are characterized by a rapid loss of fog upon chemical bleaching. To illustrate, a sample of Emulsion Coatings A and B is bleached before development in a chemical bleach having the following composition:

Potassium cyanide50 mg. Acetic acid (glacial)3.47 cc. Sodium acetatell.49 g. Potassium bromide119 mg. Water to 1 liter.

The film samples are bleached for 10 minutes at 68 degrees F. in the above bleach without agitation. Coatings are then washed in running water for 10 minutes and allowed to dry at room temperature. The coatings are then developed for 6 minutes in Kodak DK-SO developer,'

fixed, washed and dried in the conventional manner. Each of the film samples exhibits more than a 45% loss in maximum density upon bleaching.

EXAMPLE III Color forming couplers can be incorporated into the direct-positive photographic silver halide emulsions described herein. To illustrate, the dyes indicated in the following Table 2 are added to samples of the reduction and gold fogged silver bromoiodide emulsion of Example I which contains the electron acceptor S-m-nitrobenzylidenerhodanine (Emulsion A) and the emulsion is digested TABLE 2 Color of dye Reg on oi formed by Type of Coating Dye (g./mole) sensitization Color forming coupler Exposure coupler process 1 None Blue a-benZoy -3-[a-(2,4-d myl- Tungsten source Yellow A phenoxy) butyramidel-2- Wratten No. methoxyacetanilide. 35 +38A filters. 2 Anhydro-Y-ethyl-3-(3- Green l-(2,4,5-trichloro-phenyl)-3,3- Tungsten source Magenta A sulfobutyl) thia-2-cyanine (2",4"-di-t-amylphenoxyacet- Wratten No. hydroxide (0.2) anhydro-lamide) benzimidazo-fi- 61 +16 filter. ethyl-l-(4-sulfobutyl)-2,2- pyrazolone. cyanine hydroxide (0.2). 3 3,3-dirnethyl-8,10,di Red 5-[a-(2,4di-t-amyl-phenoxy) Tungsten source Cyan A (1n-toloxy)thiacrabohexanamido]-2-heptatluorobu- Wratter N o. 20 cyanine bromide (0.2). tyramidophenol-l-hydroxy-2 filter.

[ o.-(2,4-di-t-amylphenoxy-nbutyl)]-na thamide. 4 3,3-dimethyl-8,l-dl- Red 1-hydroxy-2- -(2- Daylight quality Cyan B (m-toloxy) thiacarbocyanine bromide (0.2).

A-Reversal color process as described in Graham et acetamido) -phenethyl]- naphthalamide.

source Wratten No. 16 filter.

a1. U.S. Patent 3,046,129, issued July 24, 1962 in Example (a) (col. 27, lines 25 et seq.) except that black-and-white (MQ) development is omitted and the color development is reduced to 1 minute and done in total darkness until after fixing.

BColor process for developing cyan dye images as described in Vittum et a1. U.S. Patent 3,002,836 issued October 3, 1961 in Example III (col. 4, lines 5 et seq.) except that black-and-white (MQ) development is omitted.

EXAMPLE IV Any of the photographic silver halides can be used in the fogged direct-positive photographic emulsions of this invention. To illustrate, the following photographic emusions are prepared:

Photographic silver bromide emulsion (Emulsion A) A monodispersed silver bromide photographic emulsion is prepared by adding an aqueous solution of potassium bromide and an aqueous solution of silver nitrate simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 degrees C. over a period of approximately 35 minutes. The pH is maintained at about 2 and the pAg at about 8.5 during the addition. The resulting photographic emulsion is reduction and gold fogged by first adding 025 mg. of thiourea dioxide and heating the emulsion for 60 minutes at 65 degrees C. and then adding 4 mg. of potassium chloroaurate and heating for approximately 35 minutes at 65 degrees C. One-hundred mg. of an electron accepting compound (5-m-nitrobenzylidenerhodanine) is added to the emulsion.

Photographic silverchlorobromide emulsion (Emulsion B) A monodispersed silver chlorobromide emulsion containing 20 mole percent chloride is prepared by adding an aqueous solution of potassium bromide and potassium chloride and an aqueous solution of silver nitrate simultaneously to a rapidly agitated aqueous gelatin solution at a temperature of 70 degrees C. over a period of about 35 minutes. The pH is maintained at about 2 and the pAg at about 7.9. The photographic emulsion is reduction and gold fogged by first adding 0.5 mg. thiourea dioxide and heating the emulsion for 60 minutes at 65 degrees C. and then adding 4 mg. potassium chloroaurate and heating for 60 minutes at 65 degrees C. One hundred mg. of an electron accepting compound (5-m-nitrobenzylidenerhodanine) is added to the emulsion. In each of Emulsions A and B the average grain size is about 0.2 micron. As shown by electron micrographs, less than 5%, by number, of the coarse silver halide grains, i.e., silver halide grains larger than the mean grain size, are more than 40% larger in diameter than the mean grain diameter. A sample of each of Emulsions A and B is coated on cellulose acetate support at a coverage of 100 mg. of silver and 250 mg. of gelatin per square foot of support. Samples of each of the coatings are exposed and processed as described in Example I. The following results are obtained:

EXAMPLE V As previously indicated, a preferred direct-positive photographic silver halide emulsion of this invention comprises silver halide grains of substantially uniform diameter which grains are reduction and gold fogged with a low concentration of reduction fogging agent. In such a procedure it is most desirable to also employ a relatively low concentration of gold fogging agent since increasing concentrations of gold fogging agent generally decrease photographic speed. To illustrate, the fine grain cubic silver bromoiodidc emulsions of Example I (Emulsion A) is reduction fogged by first adding 0.25 mg. of thiourea dioxide per mole of silver halide and heating the emulsion for 60 minutes at 65 degrees C. This emulsion is then divided into several portions and varying concentrations of potassium chloroaurate, as listed in the following Table 4, are added to each portion of the emulsion and each portion is heated for 60 minutes at 65 degees C. Five-hundred mg. per mole of silver halide of an electron accepting compound which is an imidazo-quinoxaline dye of the type disclosed in Brooker et al., Belgian Patent 660,253, published Mar. 15, 1965, is added to each portion of the emulsion. A sample of each portion of the emulsion is coated on a cellulose acetated film support at a coverage of mg. of silver and 250 mg. of gelatin per square foot of support. A sample of each coating is exposed and processed as in Example I. The following results are obtained:

TABLE 4 Potassium ehloroau- Coating N0. rate (mg/mole AgX) Relative speed Prior art direct-positive photographic silver halide emulsions comprising silver halide; grains which are fogged with a combination of a reducing agent and a gold compound or a compound of a metal more electropositive than silver, as described in British Patent 723,019, exhibit only low photographic speed, for example, photographic speed comparable to that of photographic emulsions used in conventional enlarging papers. Such a photographic speed, on the relative scale set forth in the above Table 4, is only 10. Thus, it can be seen that the direct-positive photographic sliver halide emulsions disclosed herein exhibit a truly outstanding increase in photographic speed in comparison to such art direct-positive photographic silver halide emulsions.

Thus, by the practice of this invention there is provided direct-positive photographic silver halide emulsions exhibiting excellent photographic speed. Such emulsions are preferably prepared using reduction and gold fogging agents in combination at low concentrations. Due to their increased photographic speed, the direct-positive photographic silver halide emulsions disclosed herein are particularly useful in a variety of applications in the photographic field. For example, they can be used in lithographic printing plates, particularly those of the type disclosed US. Patent 3,146,104, issued Aug. 25, 1965, in color transfer materials, direct reversal color processes, duplicating film, e.g., microfilm, etc. If desired, the silver halide grains can be gold fogged using special processing techniques, for example, a coating of a reduction fogged silver halide, emulsion containing an electron acceping compound can be exposed and bathed in a solution of' a gold salt such as gold thiocyanide which can contain a small concentration, for example, less than about 0.5%, of a halogen such as bromide. The coating can then be processed in an alkaline developer such as Kodak DK-SO or Kodak DK- 19 developer for 10 minutes at 68 degrees F. Another interseting reversal system involves developing, in a fogging developer, a photographic silver halide emulsion which has been treated with a reduction fogging agent such as stannous chloride. This system involves exposing and developing the aforesaid photographic emulsion in an alkaline fogging developer such as Kodak DK-SO developer to which small concentrations, for example, up to about 0.2 gram per liter of triethylenetetramine and 1-phenyl-3-pyrazolidone have been added to obtain a reversal image.

The fogged direct-positive photographic silver halide emulsions described herein can also be used in negative azo dye image formation. The art of bleaching an azo dye by chemistry involving the oxidation of metallic silver is well known. In such methods an azo dye in a coating containing a stepwise image of metallic silver is bleached proportional to the silver under strongly acidic conditions giving a reversal image in dye. Bleaching rates are enhanced by accelerators such as 2-hydroxy- 3-amino phenazine or anthraquinone-p-sulfonic acid as shown, for example at p. 643 of Photographic Chemistry, English language edition, vol. 2 by Pierre Glafkides. This type of bleaching process can employ a very fine grain direct-positive photographic silver halide emulsion of the type described herein. Exposure, development in an alkaline developer such as Kodak DK-SO developer and fixation give a direct-positive silver image with no effect on the azo dye. Conventional dye-bleaching, silver bleaching and fixation then give a dye image reversal of the silver image and also a dye reversal of the original subject with an excellent ratio of D max. to D min.

As shown herein, color forming couplers can be incorporated into the direct-positive photographic silver halide emulsions of this invention. It has been found that the incorporation of a color forming coupler or coupler solvent in the emulsion significantly improves the quality of the reversal obtained in black and white elon-hydroquinone type developers. There is obtained an increase in contrast and a lower minimum density using this type developer with such emulsions.

The fogged, direct-positive photographic silver halide emulsions can also be used in color diffusion transfer systems in combination with dye developers. Photographic developers which contain a dye moiety can, of course, be synthesized. Upon applying an alkaline solution to an imagewise exposed negative developing silver halide emulsion element containing one of these dye developers, the dye developer becomes immobilized within the element where development occurs, that is, in the exposed areas. When an alkaline treated sample of this material is brought into contact with a receiver sheet, there is obtained a positive transfer print composed of transferred dye-developer and a negative printt composed of non-transferred dye developer when the nagative silver image is bleached. Dye developer coatings made with a reversal emulsion of the type disclosed herein will develop to yield a positive silver image. Therefore,

an alkaline treated sample of this material brought in contact with a receiver will yield a negative dye transfer print composed of transferred dye-developer and a positive print composed of non-transferred dye developer when the positive silver image is bleached.

The fogged, direct-positive photographic silver halide emulsions of this invention can also be used in reversal chemical transfer print by either the one-sheet system, is often used for making positive copies from positive originals and is very popular since stable right-reading images are readily obtained. The negative is exposed in a normal manner, then passed through a solvent developer in contact with a nuclated receiver. The exposed negative silver is developed, while the unexposed silver halide dissolves and diffuses to the receiver sheet where it is deposited on the nuclei and developed. The chemical transfer print can be obtained in a short time since no additional processing steps are necessary. The fogged, direct-positive photographic silver halide emulsions of this invention, upon exposure to a negative image followed by development, give a negative silver image in the emulsion layer. In the presence of a solvent developer, the exposed silver halide which has not developed, migrates to the nucleated receiver where it is deposited as a positive image. The emulsions of this invention can be used in chemical transfer processes employed to make a chemical transfer print by either the one-sheet system, in which the emulsion is coated on the same support as the receiver layer, or by the two-sheet system, in which the emulsion and receiver layers are coated on separate supports.

The direct-positive photographic silver halide emulsions of this invention can also be processed in the pres ence of ammonia vapors or other gaseous compounds of the type disclosed in U.S. Patent 3,158,481, issued Nov. 24, 1964; US. Patent 3,144,334, issued Aug. 11 1964, and British Patent 973,965, published Nov. 4, 1964. The developing agent can be incorporated into the emulsion coating or in a separate sheet. Ammonia or another gaseous compound which is used to activate the coating can be incorporated in a separate layer of the element containing the emulsion. The ammonia or other activator can be in any suitable form, for example, in the form of an ammonia polymer. Such activating materials can also be incorporated in a sheet separate from the element containing the emulsion and activated by heat. Processing with ammonia or other activators is of special interest in the document copying field where the emulsion is coated on paper or as a film duplicating material where the emulsion is coated on film.

Certain of the direct-positive photographic silver halide emulsions of this invention are capable of being used as a negative material by increasing exposure. Thus, a fine grain cubic silver bromide photographic emulsion which has been reduction and gold fogged using a low concentration of the fogging agents, as disclosed herein, can be first treated with an electron accepting compound and subsequently treated with an orthochromatic sensitizing dye such as a thiazolinerhodanine merocyanine to obtain a suitable photographic emulsion for this purpose. The orthochromatic sensitizing dye is generally used in a concentration substantially in excess of the electron accepting compound, e.g., it is generally used at a concentration which is about double the concentration of the electron accepting compound. When exposed in the projection speed range such an emulsion gives a directpositive image. Upon increasing exposure a negative image is produced.

If desired, the direct-positive photographic silver halide emulsions described herein can be blended to modify photographic properties. For example, fogged direct positive silver halide emulsions differing in sensitivity and/or contrast can be blended to produce direct positive materials having a wider exposure latitude.

Although the invention has been described in considerable detail with reference to certain \preferred embodiments thereof, it will be understood that variations and modifi'cations can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A monodispersed direct-positive photographic silver halide emulsion comprising reduction and gold fogged silver halide grains wherein the halide of said silver halide grains is at least about 50 mole percent bromide and wherein at least 95%, by weight or by number, of the silver halide grains are of a size which is within about 40% of the mean grain size.

2. A monodispersed direct-positive photographic silver halide emulsion comprising reduction and gold fogged silver halide grains wherein the halide of said silver halide grains is less than about 10 mole percent iodide and wherein at least 95%, by weight or by number, of the silver halide grains are of a size which is within about 40% of the mean grain size.

3. A direct-positive photographic emulsion according to claim 2 comprising a desensitizer which has an anodic polarographic half-wave potential and a cathodic polarographic half-wave potential which, when added togeher, give a positive sum.

4. A direct-positive photographic emulsion according to claim 2 wherein said silver halide grains are cubic grains having an average grain size in the range of about 0.01 to about 2 microns.

5. The photographic emulsion of claim 2 in which the grains are fogged with about 0.0005 to about 0.06- milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent.

6. The photographic element of claim 3 in which said desensitizer is an organic compound which spectrally sensitizes in the range of about 480 to about 800 III 1..

7. The photographic emulsion of claim 5 in which the ratio of gold fogging agent to reduction fogging agent is in the range of about 1:3 to about 20:1.

8. The photographic emulsion of claim 3 in which the silver halide comprises at least 50 mole percent bromide and said desensitizer is a cyanine dye.

9. The photographic emulsion of claim 3 which contains a spectral sensitizing dye in addition to said desensitizer.

10. A monodispersed direct-positive photographic silver halide emulsion comprising fogged silver halide grains and an organic desensitizer compound which has an anodic polarographic half-wave potential and a cathodic polarographic half-wave potential which, when added together, give a positive sum and wherein the halide of said silver halide grains is less than about mole percent iodide and at least 95% by weight or by number, of the silver halide grains are of a size which is within about 40% of the mean grain size.

11. A monodispersed direct-positive photographic silver halide emulsion comprising fogged silver halide grains and an organic desensitizer compound which has an anodic polarographic half-Wave potential and a cathodic polarographic half-wave potential which, when added together, give a positive sum and wherein the halide of said silver halide grains is at least about 50 mole percent bromide and at least 95%, by weight or by number, of the silver halide grains are of a size which is within about 40% of the mean grain size.

12. A photographic element comprising a support and at least one direct-positive photographic silver halide layer which comprises monodispersed, reduction and gold fogged silver halide grains wherein the halide of said silver halide grains is at least about 50 mole percent bromide and wherein at least 95 by weight or by number, of said silver halide grains are of a size which is within about 40% of the mean grain size.

13. A photographic element comprising a support and at least one direct-positive photographic silver halide layer which comprises monodispersed, reduction and gold fogged silver halide grains wherein the halide of said silver halide grains is less than about 10 mole percent iodide and wherein at least by weight or by number, of said silver halide grains are of a size which is within about 40% of the mean grain size.

14. A photographic element according to claim 13 wherein said silver halide layer comprises an organic desensitizer which has an anodic polarographic half-wave potential and a cathodic half-wave potential which, when added together, give a positive sum.

15. The photographic element of claim 14 in which said desensitizer is an imidazoquinoxaline dye.

16. The photographic element of claim 13 in which said silver halide comprises at least 50 mole percent bromide and the silver halide grains are fogged with about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent, the ratio of gold fogging agent to reduction fogging agent being in the range of about 1:3 to about 20:1.

17. The photographic element of claim 13 in which said silver halide grains are cubic grains having a mean grain size in the range of about 0.01 to about 2 microns, said grains in said emulsion being such that a test portion thereof, when coated as a photographic silver halide emulsion on a support to give a maximum density of at least about 1 upon processing for 6 minutes at about 68 F. in Kodak DK-SO developer, has a maximum density which is at least about 30% greater than the maximum density of an identical coated test portion which is processed for 6 minutes at about 68 F. in Kodak DK-50 developer after being bleached for about 10 minutes at about 68 F. in a bleach composition of:

Potassium cyanide-50 mg. Acetic acid (glacial)3.47 cc. Sodium acetate--1l.49 g. Potassium bromide-119 mg. Water to 1 liter.

18. The photographic element of claim 13 in which said reduction fogging agent is thiourea dioxide and the gold fogging agent is potassium chloroaurate. I

19. The photographic element of claim 13 in which said reduction fogging agent is thiourea dioxide and the gold fogging agent is auric trichloride.

20. The photographic element of claim 13 which comprises, contiguous to the silver halide grains, a color-forming coupler.

21. The process which comprises contacting (1) silver halide grains, at least 95 by weight, of which have a size which is within about 40% of the main grain size, with (2) about 0.0005 to about 0.06 milliequivalent per mole of silver halide of a reduction fogging agent and about 0.001 to about 0.01 millimole per mole of silver halide of a gold fogging agent (3) at a temperature in the range of about 40 to about C., the ratio of gold fogging agent to reduction fogging agent being in the range of about 1:3 to about 20:1.

22. The process of claim 21 in which the silver halide comprises at least 50 mole percent bromide and has a mean grain size in the range of about 0.01 to about 2 microns.

23. The process of claim 21 in which the silver halide grains are contacted with the reduction fogging agent and are subsequently contacted with the gold fogging agent.

-24. The process of claim 21 in which the reduction fogging agent is thiourea dioxide and the gold fogging agent is potassium chloroaurate.

17 18 25. The process of claim 21 comprising adding a de- OTHER REFERENCES sensitizer to the silver halide grains after they have been Adsorption of sensitizing Dyes at Definite crystal contacted with the Eduction and gold fogging l Faces, by Gunther et al., in Journal of Photographic wherein said desensitlzer has an anodic polarographic Science VOL 13 1965 280 half-wave potential and a cathodic half-wave potential 5 which, when added together, give a positive sum. NORMAN G, TQRCHIN, Primary Examiner Ref Cit d R. E. FIGHTER, Assistant Examiner FOREIGN PATENTS US. Cl. X.R.

723,019 2/1952 Great Britain. 10 96101, 107

1,169,290 4/1964 Germany.

(5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,501,305 Dated March I'Z, 1970 Inventor(s)Bernard D. Illingsworth It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 1+8, "developed" should read ---developer----T Column 6, line 51 "in dole" should read ---indole---. Column 7, first formula, that portion set forth as CH should read 1 I 1 Me Me fourth formula, the extreme right portion of the formula set forth as line 14.7, "L -nitro-6-chlorobenzotrazle" should read Lp-nitro-- -chlorobenzotriazole line 59, that portion of formula set forth as "-dimethylaminophenyliminoethyl-" should read -dimethylaminophenyliminomethyl- Column 9, line 14.6, "cubeoctahedral" should read cubo-octahedral Columns 11-12, Table 2, under heading of Dye (g./mole), the dye for Coating 3 set forth as "3,3' -dimethyl-8,10, di (m-toloxy)thiaorabooyanine bromide (0.2)" should read 3,3'-dimethyl-8,10-di (m-toloxy)- thiacarbocyanine bromide (0.2) under heading of Color forming coupler, that part of formula for Coating 2 set forth as "1 (2,L .,5-" should read 1- (2,L .,6- under heading of Exposure, for Coating 3, "Wratter" should read ---Wratten---; following Table 2, for T e of process B-, "lines 5 et seq. should read ---lines 5 et seq. Column 12, line 32, "emulsions" should read ---emulsion---; line 145, "acetated" should read ---acetate---; line 67, "sliver" should read ---silver---;

should read Page 1 of 2 pages UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3 ,50l,305 March 17, 1970 Patent No. Dated Invent0r($) Bernard Di Illin gsworth Page 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

line 70 before "art", insert prior Column 13, line 12 "accep ng" should read accepting line 39, 'interseting" should read interesting Column 14 9 line 8, delete "print by either the one-sheet system," and insert systems. The chemical transfer system line 13, 'nuclated" should read nucleated Column 15 line 25 'togeher" should read together Column 16, line 57 "main" should read mean Signed and sealed this llth day of August 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer WILLIAM E. SCHUYLER, JR. Commissioner of Patents F ORM PO-105O (10-69) UJ. GOVIINHIIIT PR NTING OFFICE 1 "ll O-Sii-l54 

